This invention relates to the provision of logic circuitry by implementing the properties of magnetic quantum dots.
The integration density of silicon electronic devices such as microprocessors has followed steady exponential growth during the last forty years. While there is still much potential for future growth of silicon integration, a point will eventually come when further increase in integration density will become impossible. There is therefore a need to provide alternatives for digital logic. Ideally, one might like to move to molecular electronics where single molecules or atoms are used as logic gates and interconnect. There are, however, sufficient technological and scientific difficulties to be overcome in this field and so it is unlikely to replace silicon electronics directly. Much interest has recently been focussed on electronic quantum dots and single electron transistors as candidates for continuing the growth of integration density beyond that of conventional silicon devices. A particularly interesting configuration of quantum dots called a quantum cellular automaton (QCA) has shown the ability to perform logic operations. Unfortunately, these devices currently only work at very low temperatures.
According to the present invention there is provided a logic device formed from at least one chain of dots of magnetic material, each dot having a width of 200 nm or less and being spaced at a distance that is sufficiently small to ensure magnetic interaction of adjacent dots. The dots may be 100 nm or less, or 80 nm or less.
The dots may have a circular shape, an elliptical shape or a combination thereof.
The dots may be formed from a soft magnetic material, such as permalloy (Ni 80 Fe 20) or Co Fe.
The dots may be formed on a substrate formed from a material such as silicon.
The logic device may also comprise means for providing one or more controlled magnetic fields to the chain of dots. The means for providing a magnetic source may include means for controlling the source that the magnetic field or fields can operate as a controlling clock. In such a device plural chains may be arranged to provide OR gates, AND gates, NOT gates, a combination thereof, or any one of a number of other logic gates. Such a device may provide an electrical output or outputs by further comprising one or more components generating a magneto-electrical effect.
The present invention provides QCA using magnetic quantum dots. The design works well up to the Curie temperature of ferromagnetic metals (xcx9c1000K) and can be implemented with dots as large as 200 nm or as small as 10 nm. The invention therefore provides magnetic quantum cellular automata (MQCA) which can bridge the gap between conventional silicon devices and molecular electronics. 200 nm dots offer an increase in areal integration density (effective number of transistors per chip) of 400 times over today""s CMOS; 10 nm dots offer a factor of 160000. Moreover, the fabrication of employing MQCA devices is relatively straightforward when compared with today""s CMOS processes. MQCA according to the invention can therefore radically alter the economics of IC manufacturing, allowing smaller companies who cannot raise the capital for a CMOS fabrication (xcx9cUS$2 Billion) to enter the market. In addition, being all magnetic, MQCA is well poised to interface to the emerging technology of Magnetic Random Access Memory (MRAM) which is set to replace all semiconductor computer memory in coming years.